Thermal Insulators and Methods Thereof

ABSTRACT

The provided articles and methods use a non-woven fibrous web containing 60-100 wt % of oxidized polyacrylonitrile fibers; and 0-40 wt % of reinforcing fibers having outer surfaces comprised of a polymer with a melting temperature of from 100° C. to 300° C. The non-woven fibrous web has an average bulk density of from 15 kg/m3 to 50 kg/m3, with the plurality of fibers substantially entangled along directions perpendicular to a major surface of the non-woven fibrous web. Optionally, the oxidized polyacrylonitrile fibers can have a crimped configuration. Advantageously, these articles can display a combination of low thermal conductivity, high tensile strength, and flame resistance.

FIELD OF THE INVENTION

Provided are articles for use in thermal insulation. The providedarticles may be used as thermal insulators in automotive and aerospaceapplications such as battery compartments for electric vehicles.

BACKGROUND

Thermal insulators reduce heat transfer between structures either inthermal contact with each other or within range of thermal convection orradiation. These materials mitigate the effects of conduction,convection, and/or radiation, and can thus help in stabilizing thetemperature of a structure in proximity to another structure atsignificantly higher or lower temperature. By preventing overheating ofa component or avoiding heat loss where high temperatures are desired,thermal management can be critical in achieving the function andperformance demanded in widespread commercial and industrialapplications.

Thermal insulators can be particularly useful in the automotive andaerospace areas. For example, internal combustion engines of automobilesproduce a great deal of heat during their combustion cycle. In otherareas of the vehicle, thermal insulation is used to protect electroniccomponents sensitive to heat. Such components can include, for example,sensors, batteries, and electrical motors. To maximize fuel economy, itis desirable for thermal insulation solutions to be as thin andlightweight as possible while adequately protecting these components.Ideally, these materials are durable enough to last the lifetime of thevehicle.

The demand for suitable insulating materials has intensified with theadvent of electric vehicles (“EVs”). EVs employ many lithium ionbatteries that perform optimally within a defined temperature range,more particularly around ambient temperatures. EVs generally have abattery management system that activates an electrical heater if thebattery temperature drops significantly below optimal temperatures andactivates a cooling system when the battery temperature creepssignificantly higher than optimal temperatures.

SUMMARY

Operations used for heating and cooling EV batteries can substantiallydeplete battery power that would otherwise have been directed to thevehicle drivetrain. During winter months, temperatures might dip as lowas −30° C., while road temperatures in summer months can exceed 65° C.Just as a blanket provides comfort by conserving a person's body heat incold weather, thermal insulation passively minimizes the power requiredto protect the EV batteries in extreme temperatures.

Developers of insulation materials for EV battery applications faceformidable technical challenges. For instance, EV battery insulationmaterials should display low thermal conductivity while satisfyingstrict flame retardant requirements to extinguish or slow the spread ofa battery fire. A common test for flame retardancy is the UL-94V0 flametest. It is also desirable for a suitable thermal insulator toresiliently flex and compress such that it can be easily inserted intoirregularly shaped enclosures and expand to occupy fully the spacearound it. Finally, these materials should display sufficient mechanicalstrength and tear resistance to facilitate handling and installation ina manufacturing process.

The provided articles and methods address these problems using anentangled non-woven fibrous web containing thermally-insulating fibersincluding oxidized polyacrylonitrile fibers and, optionally, one or morereinforcing fibers. The fibers are entangled in directions perpendicularto the major surface of the non-woven fibrous web to impart strength tothe material and prevent swelling upon exposure to flame treatment. Thereinforcing fibers can at least partially melt when heated to form abonded web with enhanced strength. Optionally, one or both sets offibers have a crimped configuration to provide greater web thickness andreduce bulk density.

In a first aspect, a thermal insulator is provided. The thermalinsulator comprises: a non-woven fibrous web comprising a plurality offibers, the plurality of fibers comprising: 60-100 wt % of oxidizedpolyacrylonitrile fibers; and 0-40 wt % of reinforcing fibers having anouter surface comprised of a polymer with a melting temperature of from100° C. to 300° C., wherein the non-woven fibrous web has an averagebulk density of from 15 kg/m³ to 50 kg/m³ and wherein the plurality offibers are substantially entangled along directions perpendicular to amajor surface of the non-woven fibrous web.

In a second aspect, a thermally insulated assembly is provided,comprising: a heat source; and an aforementioned thermal insulator atleast partially surrounding the heat source.

In a third aspect, a method of making a thermal insulator is provided,comprising: mixing oxidized polyacrylonitrile fibers having crimpedconfigurations with reinforcing fibers having outer surfaces comprisedof a polymer with a melting temperature between 100° C. and 300° C.;heating the fiber mixture to a temperature sufficient to melt the outersurfaces of the reinforcing fibers to provide a non-woven fibrous web;and entangling the oxidized polyacrylonitrile fibers and reinforcingfibers with each other along a direction perpendicular to the non-wovenfibrous web to provide an average bulk density of from 10 kg/m³ to 35kg/m³ in the non-woven fibrous web.

In a fourth aspect, a method of making a thermal insulator is provided,comprising: mixing oxidized polyacrylonitrile fibers with reinforcingfibers having outer surfaces comprised of a polymer with a meltingtemperature between 100° C. and 300° C. to obtain a non-woven fibrousweb, wherein the oxidized polyacrylonitrile fibers represent over 85% byvolume of fibers present that are not reinforcing fibers; heating thefiber mixture to a temperature sufficient to melt the outer surfaces ofthe reinforcing fibers to provide a non-woven fibrous web; andentangling the oxidized polyacrylonitrile fibers and reinforcing fiberswith each other along a direction perpendicular to the non-woven fibrousweb to provide an average bulk density of from 10 kg/m³ to 50 kg/m³ inthe non-woven fibrous web.

In a fifth aspect, a method of insulating an electric vehicle battery isprovided, comprising: providing an enclosure adjacent to the electricvehicle battery; placing an aforementioned thermal insulator incompression within the enclosure; and allowing the thermal insulation toexpand and substantially fill the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

As provided herein:

FIGS. 1-4 are side cross-sectional views of thermal insulators accordingto various exemplary embodiments.

FIG. 5 is a side cross-sectional view of a thermally insulated EVbattery assembly.

Repeated use of reference characters in the specification and drawingsis intended to represent the same or analogous features or elements ofthe disclosure. It should be understood that numerous othermodifications and embodiments can be devised by those skilled in theart, which fall within the scope and spirit of the principles of thedisclosure. Drawings may not be to scale.

Definitions

As used herein:

“Ambient conditions” means at 25° C. and 101.3 kPa pressure.

“Average” means number average, unless otherwise specified.

“Copolymer” refers to polymers made from repeat units of two or moredifferent polymers and includes random, block and star (e.g. dendritic)copolymers.

“Median fiber diameter” of fibers in a non-woven fibrous web isdetermined by producing one or more images of the fiber structure, suchas by using a scanning electron microscope; measuring the transversedimension of clearly visible fibers in the one or more images resultingin a total number of fiber diameters; and calculating the median fiberdiameter based on that total number of fiber diameters.

“Non-woven fibrous web” means a plurality of fibers characterized byentanglement or point bonding of the fibers to form a sheet or matexhibiting a structure of individual fibers or filaments which areinterlaid, but not in an identifiable manner as in a knitted fabric.

“Polymer” means a relatively high molecular weight material having amolecular weight of at least 10,000 g/mol.

“Size” refers to the longest dimension of a given object or surface.

“Substantially” means to a significant degree, as in an amount of atleast 30%, 40, 50, 60, 70, 80, 90, 95, 96, 97, 98, 99, 99.5, 99.9,99.99, or 99.999%, or 100%.

“Thickness” means the distance between opposing sides of a layer ormultilayered article.

DETAILED DESCRIPTION

As used herein, the terms “preferred” and “preferably” refer toembodiments described herein that can afford certain benefits, undercertain circumstances. However, other embodiments may also be preferred,under the same or other circumstances. Furthermore, the recitation ofone or more preferred embodiments does not imply that other embodimentsare not useful, and is not intended to exclude other embodiments fromthe scope of the invention.

As used herein and in the appended claims, the singular forms “a,” “an,”and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a” or “the” component mayinclude one or more of the components and equivalents thereof known tothose skilled in the art. Further, the term “and/or” means one or all ofthe listed elements or a combination of any two or more of the listedelements.

It is noted that the term “comprises” and variations thereof do not havea limiting meaning where these terms appear in the accompanyingdescription. Moreover, “a,” “an,” “the,” “at least one,” and “one ormore” are used interchangeably herein. Relative terms such as left,right, forward, rearward, top, bottom, side, upper, lower, horizontal,vertical, and the like may be used herein and, if so, are from theperspective observed in the particular drawing. These terms are usedonly to simplify the description, however, and not to limit the scope ofthe invention in any way.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention. Whereapplicable, trade designations are set out in all uppercase letters.

A thermal insulator according to one embodiment of the invention isillustrated in FIG. 1 and hereinafter referred to by the numeral 100.The thermal insulator 100 includes a non-woven fibrous web 102 havingopposed first and second major surfaces 104, 106.

The non-woven fibrous web 102 is comprised of a plurality of fibers,including oxidized polyacrylonitrile fibers 108. Oxidizedpolyacrylonitrile fibers 108 include those available under the tradedesignations PYRON (Zoltek Corporation, Bridgeton, Mo.) and PANOX (SGLGroup, Meitingen, GERMANY).

The oxidized polyacrylonitrile fibers 100 are derived from a polymericprecursor that contains acrylonitrile and one or more co-monomers.Useful co-monomers include, for example, methyl methacrylate, methylacrylate, vinyl acetate, and vinyl chloride. The co-monomer(s) may bepresent in an amount of up to 15 wt %, 14 wt %, 13 wt %, 12 wt %, 11 wt%, 10 wt %, 9 wt %, or 8 wt %, relative to the overall weight of thepolymeric precursor.

Oxidation of the precursor fibers can be achieved by first stabilizingthe precursor fibers at high temperatures to prevent melting or fusionof the fibers, carbonizing the stabilized fibers to eliminate thenon-carbon elements and finally a graphitizing treatment at even highertemperatures to enhance the mechanical properties of the non-wovenfibers. The oxidized polyacrylonitrile fibers 100 may be partially orfully oxidized.

Stabilization can be carried out by controlled heating of the precursorfiber in air or some other oxidizing atmosphere. Oxidation typicallytakes place at temperatures in the range of from 180° C. to 300° C.,with a heating rate of from 1-2° C. per minute.

If desired, shrinkage of the precursor fibers can be minimized bystretching the fibers along their axis during the low-temperaturestabilization treatment. Stretching can produce oxidizedpolyacrylonitrile fibers with a high degree of preferred orientationalong the fiber axis. The stabilization process produces changes inchemical structure of the acrylic precursor whereby the material becomesthermally stable to subsequent high temperature treatments. During thisprocess, the fibers change in color to black. The black fibers arecarbonized in an inert atmosphere at high temperatures, typically from1000° C. to 1500° C., at a slow heating rate to avoid damage to themolecular order of the fiber. The fibers are given a graphitizingtreatment at high temperatures for example, above 2000° C. to 3000° C.to improve the texture of the fiber and to enhance the tensile modulusof the non-woven fibrous web 102. If desired, the strength and thetensile modulus of the fibers can be further improved by stretching atelevated temperatures.

The oxidized polyacrylonitrile fibers 108 preferably have a fiberdiameter and length that enables fiber entanglements within thenon-woven fibrous web. The fibers, however, are preferably not so thinthat web strength is unduly compromised. The fibers 108 can have amedian fiber diameter of from 1 micrometers to 100 micrometers, from 2micrometers to 50 micrometers, from 5 micrometers to 20 micrometers, orin some embodiments, less than, equal to, or greater than 1 micrometer,2, 3, 5, 7, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, or 100micrometers.

Inclusion of long fibers can reduce fiber shedding and further enhancestrength of the non-woven fibrous web along transverse directions. Theoxidized polyacrylonitrile fibers 108 can have a median fiber length offrom 10 millimeters to 100 millimeters, from 15 millimeters to 100millimeters, from 25 millimeters to 75 millimeters, or in someembodiments, less than, equal to, or greater than 10 millimeters, 12,15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, or 75 millimeters.

The oxidized polyacrylonitrile fibers 108 used to form the non-wovenfibrous web 102 can be prepared from bulk fibers. The bulk fibers can beplaced on the inlet conveyor belt of an opening/mixing machine in whichthey can be teased apart and mixed by rotating combs. The fibers arethen blown into web-forming equipment where they are formed into adry-laid non-woven fibrous web.

As an alternative, a SPIKE air-laying forming apparatus (commerciallyavailable from FormFiber NV, Denmark) can be used to prepare nonwovenfibrous webs containing these bulk fibers. Details of the SPIKEapparatus and methods of using the SPIKE apparatus in forming air-laidwebs is described in U.S. Pat. No. 7,491,354 (Andersen) and U.S. Pat.No. 6,808,664 (Falk et al.).

Bulk fibers can be fed into a split pre-opening and blending chamberwith two rotating spike rollers with a conveyor belt. Thereafter, thebulk fibers are fed into the top of the forming chamber with a blower.The fibrous materials can be opened and fluffed in the top of thechamber and then fell through the upper rows of spikes rollers to thebottom of the forming chamber passing thereby the lower rows of spikerollers. The materials can then be pulled down on a porous endlessbelt/wire by a combination of gravity and vacuum applied to the formingchamber from the lower end of the porous forming belt/wire.

Alternatively, the non-woven fibrous web 102 can be formed in anair-laid machine. The web-forming equipment may, for example, be aRANDO-WEBBER device commercially-available from Rando Machine Co.,Macedon, N.Y. Alternatively, the web-forming equipment could be one thatproduces a dry-laid web by carding and cross-lapping, rather than byair-laying. The cross-lapping can be horizontal (for example, using aPROFILE SERIES cross-lapper commercially-available from ASSELIN-THIBEAUof Elbeuf sur Seine, 76504 France) or vertical (for example, using theSTRUTO system from the University of Liberec, Czech Republic or theWAVE-MAKER system from Santex AG of Switzerland).

The non-woven fibrous web 102 includes entangled regions 110 fully orpartially extending between the first major surface 104 and the secondmajor surface 106. The entangled regions 110 represent places where twoor more discrete fibers 108 have become twisted together. The fiberswithin these entangled regions 110, although not physically attached,are so intertwined that they resist separation when pulled in opposingdirections. With the presence of the entangled regions 110, theplurality of fibers in the non-woven fibrous web 102 are substantiallyentangled along directions perpendicular to the first and second majorsurfaces 104, 106.

In some embodiments, the entanglements are induced by a needle tackingprocess or hydroentangling process. Each of these processes aredescribed in more detail below.

The non-woven fibrous web can be needle tacked using a conventionalneedle tacking apparatus (e.g., a needle tacker commercially availableunder the trade designation DILO from Dilo of Germany, with barbedneedles (commercially available, for example, from Foster NeedleCompany, Inc., of Manitowoc, Wis.) whereby the substantially entangledfibers described above are needle tacked fibers. Needle tacking, alsoreferred to as needle punching, entangles the fibers perpendicular tothe major surface of the non-woven fibrous web by repeatedly passing anarray of barbed needles through the web and retracting them whilepulling along fibers of the web.

The needle tacking process parameters, which include the type(s) ofneedles used, penetration depth, and stroke speed, are not particularlyrestricted. Further, the optimum number of needle tacks per area of matwill vary depending on the application. Typically, the non-woven fibrousweb is needle tacked to provide an average of at least 5 needletacks/cm². Preferably, the mat is needle tacked to provide an average ofabout 5 to 60 needle tacks/cm², more preferably, an average of about 10to about 20 needle tacks/cm².

Further options and advantages associated with needle tacking aredescribed elsewhere, for example in U.S. Patent Publication Nos.2006/0141918 (Rienke) and 2011/0111163 (Bozouklian et al.).

The non-woven fibrous web can be hydroentangled using a conventionalwater entangling unit (commercially available from Honeycomb SystemsInc. of Bidderford, Me.; also see U.S. Pat. No. 4,880,168 (Randall,Jr.), the disclosure of which is incorporated herein by reference forits teaching of fiber entanglement). Although the preferred liquid touse with the hydroentangler is water, other suitable liquids may be usedwith or in place of the water.

In a water entanglement process, a pressurized liquid such as water isdelivered in a curtain-like array onto a non-woven fibrous web, whichpasses beneath the liquid streams. The mat or web is supported by a wirescreen, which acts as a conveyor belt. The mat feeds into the entanglingunit on the wire screen conveyor beneath the jet orifices. The wirescreen is selected depending upon the final desired appearance of theentangled mat. A coarse screen can produce a mat having perforationscorresponding to the holes in the screen, while a very fine screen(e.g., 100 mesh) can produce a mat without the noticeable perforations.

FIG. 2 shows a thermal insulator 200 which, like insulator 100, has anon-woven fibrous web 202 with opposed first and second major surfaces204, 206. The web 202 differs from that of the prior example in that itincludes both a plurality of oxidized polyacrylonitrile fibers 208 and aplurality of reinforcing fibers 216.

The reinforcing fibers 216 may include binder fibers, which have asufficiently low melting temperature to allow subsequent melt processingof the non-woven fibrous web 202. Binder fibers are generally polymeric,and may have uniform composition or contain two or more components. Insome embodiments, the binder fibers are bi-component fibers comprised ofa core polymer that extends along the axis of the fibers and issurrounded by a cylindrical shell polymer. The shell polymer can have amelting temperature less than that of the core polymer.

As used herein, however, “melting” refers to a gradual transformation ofthe fibers or, in the case of a bi-component shell/core fiber, an outersurface of the fiber, at elevated temperatures at which the polyesterbecomes sufficiently soft and tacky to bond to other fibers with whichit comes into contact, including oxidized polyacrylonitrile fibers andany other binder fibers having its same characteristics and, asdescribed above, which may have a higher or lower melting temperature.

Certain thermoplastic materials such as polyester can become tacky whenmelted, making them suitable materials for the outer surface of a binderfiber. Useful binder fibers have outer surfaces comprised of a polymerhaving a melting temperature of from 100° C. to 300° C., or in someembodiments, less than, equal to, or greater than, 100° C., 105, 110,115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190, 200, 210,220, 230, 240, 250, 260, 270, 280, 290, or 300° C.

Exemplary binder fibers include, for example, KoSa Type 254 CELBONDwhich is a bi-component fiber with a polyester core and a copolyestersheath. The sheath component melting temperature is approximately 230°F. (110° C.). The binder fibers can also be a polyester homopolymer orcopolymer rather than a bi-component fiber.

The binder fibers increase structural integrity in the insulator 200 bycreating a three-dimensionalarray of nodes where constituent fibers arephysically attached to each other. These nodes provide a macroscopicfiber network, which increases tear strength, tensile modulus, preservesdimensional stability of the end product, and minimizesfiber shedding.Advantageously, incorporation of binder fibers can allow bulk density tobe reduced while preserving structural integrity of the non-wovenfibrous web, which in turn decreases both weight and thermalconductivity.

It was found that thermal conductivity coefficient K for the non-wovenfibrous webs 102, 202 can be strongly dependent on its average bulkdensity. When the average bulk density of the non-woven fibrous web issignificantly higher than 50 kg/m³, for example, a significant amount ofheat can be transmitted through the insulator by thermal conductionthrough the fibers themselves. When the average bulk density issignificantly below 15 kg/m³, heat conduction through the fibers issmall but convective heat transfer can become significant. Furtherreduction of average bulk density can also significantly degradestrength of the non-woven fibrous web, which is not desirable.

In exemplary embodiments, the non-woven fibrous web 102, 202 has anaverage bulk density of from 15 kg/m³ to 50 kg/m³, 15 kg/m³ to 40 kg/m³,20 kg/m³ to 30 kg/m³, or in some embodiments less than, equal to, orgreater than 15 kg/m³, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32,35, 37, 40, 42, 45, 47, or 50 kg/m³.

By so reducing the overall effects of thermal conduction and convection,it is possible to achieve surprisingly low thermal conductivitycoefficients. The non-woven fibrous web of the provided thermalinsulators can display a thermal conductivity coefficient of less than0.035 W/K-m, less than 0.033 W/K-m, less than 0.032 W/K-m, or in someembodiments, less than, equal to, or greater than 0.031 W/K-m, 0.032,0.033, 0.034, or 0.035 W/K-m, at ambient conditions according to ASTMD1518-85 (re-approved 2003). Thermal conductivity coefficients in theseranges can be obtained with the non-woven fibrous web in its relaxedconfiguration (i.e., uncompressed) or compressed to 20% of its originalthickness based on ASTM D5736-95 (re-approved 2001).

The oxidized polyacrylonitrile fibers 208 in the non-woven fibrous web202 are not combustible. Surprisingly, it was found that combustion ofthe reinforcing fibers in the FAR 25-856a flame test did not result insignificant dimensional changes (no shrinkage and no expansion) in thethermal insulator. This benefit appears to have been the effect of thefiber entanglements perpendicular to the major surface of the non-wovenfibrous web.

The oxidized polyacrylonitrile fibers 208 can be present in any amountsufficient to provide adequate flame retardancy and insulatingproperties to the insulator 200. The oxidized polyacrylonitrile fibers208 can be present in an amount of from 60 wt % to 100 wt %, 70 wt % to100 wt %, 81 wt % to 100 wt %, or in some embodiments, less than, equalto, or greater than 50 wt %, 55, 60, 65, 70, 75, 80, 85, 90, or 95 wt %,or less than or equal to 100 wt %. The reinforcing fibers 216 can bepresent in an amount of from 0 wt % to 40 wt %, 3 wt % to 30 wt %, 3 wt% to 19 wt %, or in some embodiments, equal to or greater than 0 wt %,or less than, equal to, or greater than 1 wt %, 2, 3, 4, 5, 7, 10, 15,20, 25, 30, 35, 40, 45, or 50 wt %.

Preferred weight ratios of the oxidized polyacrylonitrile fibers 208 toreinforcing fibers 216 bestow both high tensile strength to tearresistance to the insulator 200 as well as acceptable flameretardancy—for instance, the ability to pass the UL-94V0 flame test. Theweight ratio of oxidized polyacrylonitrile fibers to reinforcing fiberscan be at least 4:1, at least 5:1, at least 10:1, or in someembodiments, less than, equal to, or greater than 4:1, 5:1, 6:1, 7:1,8:1, 9:1, or 10:1.

As a further option, it is possible that the non-woven fibrous web 102,202 includes a plurality of fibers that are neither oxidizedpolyacrylonitrile fibers nor reinforcing fibers having an outer surfacecomprised of a polymer with a melting temperature of from 100° C. to300° C. Such fibers may include, for example, polyester fibers having amelting temperature exceeding 300° C. To maximize the flame retardancyof the insulator 100, 200, however, it is preferred that the oxidizedpolyacrylonitrile fibers represent over 85 vol %, over 90 vol %, or over95 vol % of the plurality of fibers that do not have an outer surfacecomprised of a polymer with a melting temperature of from 100° C. to300° C.

Optionally and as shown in the figures, the oxidized polyacrylonitrilefibers 108, 208 and reinforcing fibers 116, 216 are each crimped toprovide a crimped configuration (e.g., a zigzag, sinusoidal, or helicalshape). Alternatively, some or all of the oxidized polyacrylonitrilefibers 108, 208 and reinforcing fibers 116, 216 have a linearconfiguration. The fraction of oxidized polyacrylonitrile fibers 108,208 and/or reinforcing fibers 116, 216 that are crimped can be lessthan, equal to, or greater than 5%, 10, 15, 20, 25, 30, 40, 50, 60, 70,80, 90, or 100%. Crimping, which is described in more detail in EuropeanPatent No. 0 714 248, can significantly increase the bulk, or volume perunit weight, of the non-woven fibrous web.

FIG. 3 is directed to a thermal insulator 300 having the same featuresof insulators 100, 200 while further including smoothed surfaces 320,322 exposed on the first and second major surfaces of the insulator 300.The smoothed surfaces 320, 322 may be obtained by any known method. Forexample, smoothing could be achieved by calendaring the non-wovenfibrous web, heating the non-woven fibrous web, and/or applying tensionto the non-woven fibrous web. In some embodiments, the smoothed surfaces320, 322 are skin layers produced by partial melting of the fibers atthe exposed surfaces of the non-woven fibrous web.

In some embodiments, there may be a density gradient at the smoothedsurface 320, 322. For example, portions of the smoothed surfaceproximate to the exposed major surface may have a density greater thanportions remote from the exposed major surface. Increasing bulk densityat one or both of the smoothed surfaces 320, 322 can further enhancetensile strength and tear resistance of the non-woven fibrous web. Thesmoothing of the surface can also reduce the extent of fiber sheddingwhich would otherwise occur in handling or transporting the insulator300. Still another benefit is the reduction in thermal convection byimpeding the passage of air, and therefore thermal convection, throughthe non-woven fibrous web. The one or both smoothed surfaces 320, 322may, in some embodiments, be non-porous such that air is prevented fromflowing through the non-woven fibrous web.

FIG. 4 shows still another thermal insulator 400 with a non-wovenfibrous web 402 is comprised of a plurality of fibers, includingoxidized polyacrylonitrile fibers 408 and reinforcing fibers 416. Asindicated by the color contrast in FIG. 4, the oxidizedpolyacrylonitrile fibers 408 and reinforcing fibers 416 are coated. Thecoating on the fibers can selected from, for example, silicones,acrylates, and fluoropolymers whereby the non-woven fibrous web has anemissivity of less than 0.5. Here, “emissivity” is defined as the ratioof the energy radiated from a material's surface to that radiated from ablackbody (a perfect emitter) at the same temperature and wavelength andunder the same viewing conditions. Reducing emissivity helps lower theextent to which a material loses heat from thermal radiation.

Coating the constituent fibers of the non-woven fibrous web 402 canimpart various functional and/or aesthetic benefits. For example,coating the fibers has the effect of reinforcing the fibers, thusincreasing the overall strength of the web. Certain coating materials,such as fluoropolymers and silicones, may enhance resistance to stainingor fouling because of airborne substances becoming adhered to fibersurfaces. In some applications it can be desirable to sheath the fibersin an opaque coating, can also be used to change the color of thenon-woven fibrous web 402, which is typically black or grey because ofthe oxidized polyacrylonitrile fibers.

Other aspects of the insulators 200, 300, 400 are analogous to thosedescribed already with respect to insulator 100 and shall not berepeated here.

The non-woven fibrous webs of the thermal insulators described withrespect to FIGS. 1-4 can have any suitable thickness based on the spaceallocated for the application at hand. For common applications, thenon-woven fibrous webs can have a thickness of from 1 millimeter to 50millimeters, from 2 millimeters to 25 millimeters, from 3 millimeters to20 millimeters, or in some embodiments, less than, equal to, or greaterthan 1 millimeter, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 17, 20, 22, 25,27, 30, 35, 40, 45, or 50 millimeters.

As described previously, many factors influence the mechanicalproperties displayed by the non-woven fibrous web, including fiberdimensions, the presence of binding sites on the reinforcing fibers,fiber entanglements, and overall bulk density. Tensile strength andtensile modulus are metrics by which the properties of the non-wovenfibrous web may be characterized.

The tensile modulus is generally indicative of the stiffness of thematerial and can be from 7 kPa to 1400 kPa, 70 kPa to 550 kPa, 140 kPato 350 kPa, or in some embodiments, less than, equal to, or greater than5 kPa, 7, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140,150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000,1100, 1200, 1300, or 1400 kPa. Tensile strength represents theresistance of the non-woven fibrous web to tearing or permanentlydistorting and can be at least 28 kPa, at least 32 kPa, at least 35 kPa,or in some embodiments, less than, equal to, or greater than 28 kPa, 29,30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 42, 44, 45, 47, or 50 kPa.

Surprisingly, it was found that entangling the fibers of the non-wovenfibrous web perpendicular to the major surfaces of the web to produce amaterial having a bulk density in the range of from 15 kg/m³ to 50 kg/m³solved a technical problem associated with volumetric expansion in theUL-94V0 or FAR 25-856a flame test. Specifically, it was discovered thatwhile conventional oxidized polyacrylonitrile materials were observed toswell substantially after flame testing, the provided thermal insulatorsdo not. In some embodiments, the provided non-woven fibrous websdeviates less than 10%, less than 7%, less than 5%, less than 4%, orless than 3%, or in some embodiments, less than, equal to, or greaterthan 10%, 9, 8, 7, 6, 5, 4, or 3% in thickness after flame testing,relative to its original dimensions.

The thermal insulators 100, 200, 300, 400 may optionally includeadditional layers not explicitly shown in FIGS. 1-4. To assist ininstallation, for example, any of these exemplary thermal insulators mayfurther include an adhesive layer, such as a pressure-sensitive adhesivelayer or other attachment layer extending across and contacting thenon-woven fibrous web. As another possibility, any of these insulatorsmay include a solid thermal barrier such as an aluminum sheet or foillayer adjacent to the non-woven fibrous web. For some applications, oneor more acoustically insulating layers may also be coupled to thenon-woven fibrous web.

FIG. 5 is a schematic of a passive thermally insulated assembly 500housing an EV battery pack for an automotive application. The assembly500 can be mounted below the car chassis and held by a bottom plate 530,typically made from fiberglass. Centrally located is a battery pack 540,having a bottom surface bounded by a thermal insulator 532 such asdescribed herein. While not depicted here, additional thermal insulatorsmay be disposed along the top or any of the side surfaces of the batterypack 540.

As further shown in FIG. 5, the battery pack 540 and insulator 532 arecollectively enclosed in a case 542, which may be made from aluminum ora composite material. Additional thermal insulators 534, 536, 538, 539are disposed around the case 542 as shown, partially surrounding it toprovide further insulation from the external environment. Optionally andas shown, the case 542 has a plurality of protrusions 543 along itsbottom surface to accommodate channels for circulating a coolant. Inthis passive thermal system, the battery pack 540 acts as a heat sourceto help keep the enclosure within the case 542 within a pre-determinedtemperature range.

Thermal insulation can be installed using any suitable method. Theprovided thermal insulators are not only conformable but are capable ofbeing compressed and expanded to fill the cavities, or enclosures, inwhich they are housed. Enclosures along the outer periphery of the case542 may be irregularly shaped and/or have significant variations inthickness as shown. Enclosures used in EV applications may, in someinstances, have thickness variations in the range of from 10% to 100%relative to the largest thickness dimension of the enclosure. Theprovided thermal insulators may, in an exemplary installation, be placedin compression within such an enclosure, and then allowed to expand andsubstantially fill the enclosure.

The resilience of these materials can be characterized based on theirdimensional recovery shortly after being compressed. In preferredembodiments, for example, the thickness recovers to at least 70%, 72,75, 77, 80, 82, 85, 87, 90, 92, or 95% of its original thickness 5minutes after being compressed to 37% of its original thickness atambient conditions.

While not intended to be exhaustive, a list of exemplary embodiments isprovided as follows:

-   1. A thermal insulator comprising: a non-woven fibrous web    comprising a plurality of fibers, the plurality of fibers    comprising: 60-100 wt % of oxidized polyacrylonitrile fibers; and    0-40 wt % of reinforcing fibers having an outer surface comprised of    a polymer with a melting temperature of from 100° C. to 300° C.,    wherein the non-woven fibrous web has an average bulk density of    from 15 kg/m³ to 50 kg/m³ and wherein the plurality of fibers are    substantially entangled along directions perpendicular to a major    surface of the non-woven fibrous web.-   2. The thermal insulator of embodiment 1, wherein the non-woven    fibrous web contains 3-30 wt % of reinforcing fibers having an outer    surface comprised of a polymer with a melting temperature of from    100° C. to 300° C.-   3. The thermal insulator of embodiment 2, wherein the non-woven    fibrous web contains 3-19 wt % of reinforcing fibers having an outer    surface comprised of a polymer with a melting temperature of from    100° C. to 300° C.-   4. The thermal insulator any one of embodiments 1-3, wherein the    non-woven fibrous web has an average bulk density of from 15 kg/m³    to 40 kg/m³.-   5. The thermal insulator of embodiment 4, wherein the non-woven    fibrous web has an average bulk density of from 20 kg/m³ to 30    kg/m³.-   6. The thermal insulator of any one of embodiments 1-5, wherein the    oxidized polyacrylonitrile fibers represent over 85 vol % of the    plurality of fibers that are not reinforcing fibers.-   7. The thermal insulator of any one of embodiments 1-5, wherein at    least some of the oxidized polyacrylonitrile fibers have a crimped    configuration.-   8. The thermal insulator of any one of embodiments 1-7, wherein the    substantially entangled plurality of fibers comprise Needle tacked    fibers.-   9. The thermal insulator of any one of embodiments 1-8, wherein the    non-woven fibrous web has a thickness of from 1 millimeter to 50    millimeters.-   10. The thermal insulator of embodiment 9, wherein the non-woven    fibrous web has a thickness of from 2 millimeters to 25 millimeters.-   11. The thermal insulator of embodiment 10, wherein the non-woven    fibrous web has a thickness of from 3 millimeters to 20 millimeters.-   12. The thermal insulator of any one of embodiments 1-11, wherein    the oxidized polyacrylonitrile fibers have a median fiber diameter    of from 1 micrometers to 100 micrometers.-   13. The thermal insulator of embodiment 12, wherein the oxidized    polyacrylonitrile fibers have a median fiber diameter of from 2    micrometers to 50 micrometers.-   14. The thermal insulator of embodiment 13, wherein the oxidized    polyacrylonitrile fibers have a median fiber diameter of from 5    micrometers to 20 micrometers.-   15. The thermal insulator of any one of embodiments 1-14, wherein    the oxidized polyacrylonitrile fibers have a median fiber length of    from 10 millimeters to 100 millimeters.-   16. The thermal insulator of embodiment 15, wherein the oxidized    polyacrylonitrile fibers have a median fiber length of from 15    millimeters to 100 millimeters.-   17. The thermal insulator of embodiment 16, wherein the oxidized    polyacrylonitrile fibers have a median fiber length of from 25    millimeters to 75 millimeters.-   18. The thermal insulator of any one of embodiments 1-17, wherein    the weight ratio of oxidized polyacrylonitrile fibers to reinforcing    fibers is at least 4:1.-   19. The thermal insulator of embodiment 18, wherein the weight ratio    of oxidized polyacrylonitrile fibers to reinforcing fibers is at    least 5:1.-   20. The thermal insulator of embodiment 19, wherein the weight ratio    of oxidized polyacrylonitrile fibers to reinforcing fibers is at    least 10:1.-   21. The thermal insulator of any one of embodiments 1-20, wherein    the non-woven fibrous web has a tensile modulus of from 7 kPa to    1400 kPa.-   22. The thermal insulator of embodiment 21, wherein the non-woven    fibrous web has a tensile modulus of from 70 kPa to 550 kPa.-   23. The thermal insulator of embodiment 22, wherein the non-woven    fibrous web has a tensile modulus of from 140 kPa to 350 kPa.-   24. The thermal insulator of any one of embodiments 1-23, where the    non-woven fibrous web has a tensile strength more than 28 kPa.-   25. The thermal insulator of any one of embodiments 1-24, wherein    the non-woven fibrous web recovers to at least 70% of its original    thickness 5 minutes after being compressed to 37% of its original    thickness at ambient conditions.-   26. The thermal insulator of any one of embodiments 1-25, wherein    the non-woven fibrous web has a thermal conductivity coefficient of    less than 0.035 W/K-m in its relaxed configuration.-   27. The thermal insulator of embodiment 26, wherein the non-woven    fibrous web has a thermal conductivity coefficient of less than    0.035 W/K-m when compressed to 20% of its original thickness.-   28. A thermally insulated assembly comprising: a heat source; and a    thermal insulator of any one of embodiments 1-27 at least partially    surrounding the heat source.-   29. The assembly of embodiment 28, wherein the heat source comprises    an electric vehicle battery.-   30. A method of making a thermal insulator comprising: mixing    oxidized polyacrylonitrile fibers having crimped configurations with    reinforcing fibers having outer surfaces comprised of a polymer with    a melting temperature between 100° C. and 300° C.; heating the fiber    mixture to a temperature sufficient to melt the outer surfaces of    the reinforcing fibers to provide a non-woven fibrous web; and    entangling the oxidized polyacrylonitrile fibers and reinforcing    fibers with each other along a direction perpendicular to the    non-woven fibrous web to provide an average bulk density of from 10    kg/m³ to 35 kg/m³ in the non-woven fibrous web.-   31. A method of making a thermal insulator comprising: mixing    oxidized polyacrylonitrile fibers with reinforcing fibers having    outer surfaces comprised of a polymer with a melting temperature    between 100° C. and 300° C. to obtain a non-woven fibrous web,    wherein the oxidized polyacrylonitrile fibers represent over 85% by    volume of fibers present that are not reinforcing fibers; heating    the fiber mixture to a temperature sufficient to melt the outer    surfaces of the reinforcing fibers to provide a non-woven fibrous    web; and entangling the oxidized polyacrylonitrile fibers and    reinforcing fibers with each other along a direction perpendicular    to the non-woven fibrous web to provide an average bulk density of    from 10 kg/m³ to 35 kg/m³ in the non-woven fibrous web.-   32. The method of embodiment 30 or 31, wherein the non-woven fibrous    web has an average bulk density of from 15 kg/m³ to 30 kg/m³.-   33. The method of embodiment 32, wherein the non-woven fibrous web    has an average bulk density of from 20 kg/m³ to 30 kg/m³.-   34. The method of any one of embodiments 30-33, further comprising    smoothing a major surface of the non-woven fibrous web by    calendaring the non-woven fibrous web, heating the non-woven fibrous    web, and/or applying tension to the non-woven fibrous web.-   35. The method of embodiment 34, further comprising a density    gradient at the smoothed surface.-   36. The method of any one of embodiments 30-35, further comprising    coating the non-woven fibrous web with a coating fluid selected from    the group consisting of silicones, acrylates, and fluoropolymers    whereby the non-woven fibrous web has an emissivity of less than    0.5.-   37. The method of any one of embodiments 30-36, wherein the    resulting non-woven fibrous web passes the UL-94V0 flame test.-   38. A thermal insulator made by the method of any one of embodiments    30-37.-   39. A method of insulating an electric vehicle battery comprising:    providing an enclosure adjacent to the electric vehicle battery;    placing the thermal insulator of any one of embodiments 1-27 and 38    in compression within the enclosure; and allowing the thermal    insulator to expand and substantially fill the enclosure.-   40. The method of embodiment 39, wherein the enclosure has thickness    variations of 10% to 100%, relative to the largest thickness    dimension of the enclosure.

EXAMPLES

Objects and advantages of this disclosure are further illustrated by thefollowing non-limiting examples, but the materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

TABLE 1 Materials Designation Description Source OPAN-1 Oxidizedpolyacrylonitrile Zoltech, staple fibers, median length = Bridgeton, MO50 mm, 1.7 dtex (12 micrometers), crimp level >7.6 per inch (>3.0 percm), available under the trade designation “ZOLTEK OX STAPLE FIBERS”PET-FR Polyethylene terephthalate Trevira GmbH, (PET) staple fibers withflame Hattersheim, retardant agent, available under Germany the tradedesignation “TREVIRA CS AND FR” HT500T2 Web of polyester fibers 3M Co.,including scrim material on both St. Paul, MN major surfaces, availableunder the trade designation “3M THINSULATE HIGH TEMPERATURE ACOUSTICABSORBER HT500T2”

Test Methods

Surface Base Weight Measurement:

A section of nonwoven web was cut to a 12 inches by 12 inches (30.5 cmby 30.5 cm) square and was weighed. The weight divided by the surfacearea (0.0929 m²) gave the surface base weight, reported in grams persquare meter (“gsm”).

Nonwoven Web Thickness Measurement:

The method of ASTM D5736-95 was followed, according to test method forthickness of high loft nonwoven fabrics. The plate pressure wascalibrated at 0.002 psi (13.790 Pascal).

Average Bulk Density Measurement:

The surface base weight was divided by the sample thickness to give theaverage bulk density, reported in kg/m³.

Absolute Thermal Conductivity Coefficient Measurement (ThermalConductivity Plus Convection and Radiation):

The ASTM D1518-86 standard test method for thermal transmittance oftextile materials was followed, using a NETZSCH HFM436 machine. The topand bottom plate temperatures were set at a 20° C. delta (i.e., +10° C.and −10° C. relative to the mean temperature).

Flame Test 1:

FAR 25-853a and FAR 25-853b vertical burner. Reference to UL94-V0standard with flame height 20 mm and burn twice at 10 seconds each.

Flame Test 2:

FAR 25-856a radiant panel test.

Tensile Strength Measure:

Follow ASTM D882-12 standard and used Instron. Samples were cut 1 inch(25.4 mm) wide and 2 inches (50.8 mm) grab distance.

Comparative Example 1 (CE-1)

A sample of HT500T2 had the scrim material removed, by hand, from bothmajor surfaces, to give the web of polyester fibers that was tested asCE-1

Comparative Example 2 (CE-2)

100 wt. % OPAN, Needle tacked. 13 oz per sq yd (or 440 gsm) from SGLGroup (Charlotte, N.C.)

Comparative Example 3 (CE-3)

OPAN Supplier name is Zhenjiang Yishengyu Co. Ltd. (

), this type of OPAN is 2.5 denier and 64 mm length. The binder suppliername is SINOPEC Yizheng Chemical Fiber Co. Ltd. (

), this type of binder is 4080 (standard PET bi-component fiber, Meltyfiber). The web was made through a carding process, using 30 wt. %binder and 70 wt. % OPAN fibers.

Comparative Example 4 (CE-4)

About ⅓ of a layer of CE-3 was peeled away, by hand, and used fortesting.

Example 1 (EX-1): 90 wt. % OPAN-1+10 wt. % PET-FR, Needle Tacked

A mixture of 90% (by weight) PANOX® A140 1.7 dtex 12 micrometers), 50 mmcut length, staple fibers and 10% (by weight) TREVIRA T270 3.3 dtex (17micrometers), 60 mm cut length monocomponent FR-modified PET wereopened, blended and air-laid at 5.7 ft/min using an 18 inch wide RandoLab Series Model SB-Feeder/SBD-Webber where the Webber Lickerin wasoperating at 3000 rpm to form a 150 gsm unbonded web. This unbonded webwas conveyed to a Dilo Needle Loom, Model DI-Loom OD-1 6 having aneedleboard array of 23 rows of 75 needles/row where the rows areslightly offset to randomize the pattern. The needles are Foster 203-22-1.5B needles. The array is roughly 7 inches deep in the machinedirection and nominally 24 inches (61 cm) wide with needle spacings ofroughly 0.30 inch (7.6 mm). The needleboard was operated at 91strokes/minute to entangle and compact the web to a roughly 0.20 inch(5.1 mm) thickness. By needle tacking, physical entanglement wasintroduced in the direction perpendicular to the web's major surface.

The web was then conveyed into an electric oven (225-230° C.) with aline speed of 1.1 m/min, which melts the TREVIRA T270 3.3 dtex (17micrometers), 60 mm cut length monocomponent FR-modified PET fibers. Inthis example, the web was removed immediately after the oven. The ovenis an electric oven from International Thermal System, LLC (Milwaukee,Wis.). It has one heating chamber of 5.5 meters in length; the principleis air blowing in the chamber from the top. The circulation can be setso that a part of the blown air can be evacuated (20 to 100% setup) anda part can be re-circulated (20-100% setup). In this example, the airwas evacuated at 60% setting and re-circulated at 40%, the temperaturewas 227° C. in the chamber. The sample was passed twice in the chamber.

Example 1, Compressed (EX-1, Compressed)

The web of EX-1, having initial thickness of 5.1 mm, was squeezed to 1.9mm thickness for 60 hours, and then was allowed for about 5 minutes torecover to 3.6 mm. After 2 days, the sample recovered to 4.2 mm.

Comparative Example 5 (CE-5): 90 wt. % OPAN+10 wt. % FR Binder, NoNeedle Tacking

A nonwoven fibrous web was produced according to the procedure followedin Example 1, except that the needle tacking step was omitted.

Example 2 (EX-2): 80 wt. % OPAN+20 wt. % FR Binder, Needle Tacked

A nonwoven fibrous web was produced according to the procedure followedin Example 1, except that the weight ratio of OPAN-1 to PET-FR was80:20.

Example 2, Compressed (EX-2, Compressed)

The web of EX-2, having an initial thickness of 4.4 mm, was squeezed to1.9 mm thickness for 20 minutes, and then allowed to relax for about 1minute to 3.6 mm.

Comparative Example 6 (CE-6): 80 wt. % OPAN+20 wt. % FR Binder, NoNeedle Tacking

A nonwoven fibrous web was produced according to the procedure followedin Example 2, except that the needle tacking step was omitted.

Example 3 (EX-3): 80 wt. % OPAN+20 wt. % FR Binder, Needle Tacked, PlusSilicone Coating

A nonwoven fibrous web was prepared according to Example 2 (includingneedle tacking), and was coated with a silicone coating mixtureaccording to Table 2. The silicone coating mixture was applied byplacing all the materials of Table 2 in a pan and soaking the nonwovenfibrous web until the nonwoven fibrous web appeared to be completelysaturated by the silicone coating mixture. The silicone coating mixturewas cured on the nonwoven fibrous web in a convection oven at 105° C.for 4 minutes.

TABLE 2 Silicone coating mixture Amount, Material grams “SYL-OFF SB2792”Coating 14.63 (from Dow Corning, Midland, MI) “SYL-OFF 7048”Cross-linker 0.30 (from Dow Corning, Midland, MI) Zn-DBU-AA Catalyst0.825 Heptane 85.4

In Table 2, Zn-DBU-AA=Zinc+1,8-diazabicyclo[5.4.0]unde-7-ene+aceticanhydride (similar to those catalysts found in U.S. Pat. No. 9,006,357,the description of which is incorporated herein by reference).

Example 4: 75 wt. % OPAN+25 wt. % Binder, Needle Tacked

A non-woven fibrous web was produced according to the procedure followedin Example 1, except that the weight ratio of OPAN-1 to PET-FR was75:25.

Example 5: 75 wt. % OPAN+25 wt. % Binder, Needle Tacked, Plus SiliconeCoating, Plus Calendering Step to have a Smooth and Densified Surface

A nonwoven fibrous web with silicone coating was produced according toExample 3, except that the weight ratio of OPAN-1 to PET-FR was 75:25.The silicone-coated nonwoven fibrous web was then subjected to acalendering procedure to give the coated web with a smooth and densifiedsurface. The web was calendered between two smooth steel rolls, with thetop roll set at 219° C. and the bottom roll set at 222° C. Gap betweenthe two rolls was set at 0.030 inch (7.6 mm), with pressure at 500pounds per lineal inch (89 kg per lineal centimeter). Speed was at 3ft/min (0.91 meter/min).

Example 6: 70 wt. % OPAN+30 wt. % Binder, Needle Tacked

A mixture of 70% (by weight) PANOX® A140 1.7 dtex (12 micrometers), 50mm cut length, staple fibers and 30% (by weight) TREVIRA T270 6.7 dtex(25 micrometers), 60 mm cut length monocomponent FR-modified PET werefed into a split pre-opening and blending chamber with two rotatingspike rollers with a conveyor belt with a width of 0.6 m at a velocity0.8 m/min. The fibrous materials were opened and fluffed in the top ofthe chamber and then fell through the upper rows of spikes rollers tothe bottom of the forming chamber passing thereby the lower rows ofspike rollers. The materials were pulled down on a porous endlessbelt/wire by a combination of gravity and vacuum applied to the formingchamber from the lower end of the porous forming belt/wire. A supportlayer of the type JM 688-80 (Support Layer 1) was fed into the formingchamber on the top surface of the endless forming belt/wire running atthe lower end of the forming chamber moving at a speed of 1.1 m/min.

This unbonded web was conveyed to a Dilo Needle Loom, Model DI-Loom OD-16 having a needleboard array of 23 rows of 75 needles/row where the rowswere slightly offset to randomize the pattern. The needles were 36 gauge3½″ (8.9 cm) conical felting needles from Feltloom. The array wasroughly 7 inches (18 cm) deep in the machine direction and nominally 24inches (61 cm) wide with needle spacings of roughly 0.30 inch (7.6 mm).The needleboard was operated at 225 strokes/minute to entangle andcompact the web to a roughly 0.20 inch (5.1 mm) thickness.

The web was then conveyed into an electric oven (225° C. to 230° C.)with a line speed of 1.1 m/min, which melted the TREVIRA T270 3.3 dtex(17 micrometers), 60 mm cut length monocomponent FR-modified PET fibers.In this example, the web was removed immediately after the oven. Theoven was an electric oven from International Thermal System, LLC(Milwaukee, Wis.). It had one heating chamber of 5.5 meters in length;the principle is air blowing in the chamber from the top. Thecirculation can be set so that a part of the blown air can be evacuated(20 to 100% setup) and a part can be re-circulated (20-100% setup). Inthis example, the air was evacuated at 60% setting and re-circulated at40%, the temperature was 227° C. in the chamber. The sample was passedtwice in the chamber.

Samples were tested for flame resistance, tensile strength, and thermalconductivity, according to the described test methods, with results assummarized in Tables 3 to 6.

TABLE 3 Flame Test 1 Data Needle Surface PET- tack, Thick- base BulkFlame OPAN- FR, strokes/ ness, weight, density, Test 1 material 1, wt. %wt. % min mm gsm kg/m³ results CE-1 0 100 0 21 500 24 Failed CE-2 100 0ND 8.1 372 46 Passed CE-3 70 30 0 10.8 281 26 Passed CE-4 70 30 0 3.6 9426 Failed EX-1 90 10 91 5.1 137 27 Passed EX-1, 90 10 91 3.6 137 38Passed com- pressed CE-5 90 10 0 6.1 154 25 Passed EX-2 80 20 91 4.4 13030 Passed EX-2, 80 20 91 3.6 130 36 Failed com- pressed CE-6 80 20 0 5.8137 24 Passed EX-3 80 20 91 4 185 46 Failed EX-4 75 25 91 6.1 169 28Passed EX-5 75 25 91 9.9 234 24 Passed EX-6 70 30 225 6.0 280 47 Passed

In Table 3, “ND”=not determined; the as-received CE-2 material wasalready Needle tacked.

TABLE 4 Flame Test 2 Data for CE-3 and EX-1 Needle Surface tack, thick-base FAR 25-856a OPAN, Binder, strokes/ ness, weight, test results andSample wt % wt % min mm gsm description CE-3 70 30 0 10.8 281 Thebinders vaporized out when the sample were placed into the 520° F. (271°C.) chamber. When nozzle down, saw flame propagation until all bindersburnt out. Sample thickness doubled after burn. EX-1 90 10 10 5.1 137The binders vaporized out when the sample were placed into the 520° F.(271° C.) chamber. When nozzle down, saw flame propagation, all binderburnt out within 10 seconds. Sample was still intact after the burn. Thethickness was measured to be 5.3 mm after the burn

TABLE 5 Tensile Strength Data Surface base Bulk Weight, Thickness,weight, density, Peak Stress, Modulus, Sample grams mm gsm kg/m³ psi(kPa) psi (kPa) CE-2 34.55 8.1 371.8931 46 40.83 (281.5) 75.2 (518) CE-326.06 10.8 280.5075 26 3.69 (25.4) 29.32 (202.2) EX-1 12.72 5.1 136.916927 6.16 (42.5) 46.99 (324.0) CE-5 14.32 6.1 154.1392 25 5.42 (37.4)45.81 (315.8) EX-2 12.12 4.4 130.4586 30 15.3 (105) 126.3 (870.8) CE-612.74 5.8 137.1322 24 8.8 (61) 73.83 (506.0)

TABLE 6 Thermal Conductivity Data Surface Thick- base bulk k k k k k kness, weight, density, (W/K-m) (W/K-m) (W/K-m) (W/K-m) (W/K-m) (W/K-m)Sample mm gsm kg/m³ @ 10° C. @ 20° C. @ 30° C. @ 40° C. @ 50° C. @ 60°C. CE-1 23.2 490 21.1 0.035375 0.037554 0.038651 0.040712 0.0418390.043876 HT500T2 25.1 684 27.2 0.035701 0.037965 0.039143 0.0411310.042257 ND CE-2 8.1 372 45.6 0.032073 0.033576 0.034732 0.036124 ND NDCE-3 10.8 281 25.7 0.029218 0.030184 0.031812 0.032961 0.034561 0.035636EX-1 5.1 137 26.9 0.02647 0.027664 0.028918 0.030386 0.031792 0.033133EX-1, 2.261 137 64.7 0.023076 0.024183 0.025546 0.027128 0.0287390.030212 compressed EX-2 4.9 106 21.7 0.02667 0.028029 0.029251 0.0306340.032187 0.03365 EX-5 9.9 234 23.6 0.031118 0.032504 0.034121 0.035475ND ND

All cited references, patents, and patent applications in the aboveapplication for letters patent are herein incorporated by reference intheir entirety in a consistent manner. In the event of inconsistenciesor contradictions between portions of the incorporated references andthis application, the information in the preceding description shallcontrol. The preceding description, given to enable one of ordinaryskill in the art to practice the claimed disclosure, is not to beconstrued as limiting the scope of the disclosure, which is defined bythe claims and all equivalents thereto.

1. A thermal insulator comprising: a non-woven fibrous web comprising aplurality of fibers, the plurality of fibers comprising: 60-100 wt % ofoxidized polyacrylonitrile fibers; and 0-40 wt % of reinforcing fibershaving an outer surface comprised of a polymer with a meltingtemperature of from 100° C. to 300° C., wherein the non-woven fibrousweb has an average bulk density of from 15 kg/m³ to 50 kg/m³ and whereinthe plurality of fibers are substantially entangled along directionsperpendicular to a major surface of the non-woven fibrous web.
 2. Thethermal insulator of claim 1, wherein the non-woven fibrous web contains3-19 wt % of reinforcing fibers having an outer surface comprised of apolymer with a melting temperature of from 100° C. to 300° C.
 3. Thethermal insulator of claim 1, wherein the oxidized polyacrylonitrilefibers represent over 85 vol % of the plurality of fibers that are notreinforcing fibers.
 4. The thermal insulator of claim 1, wherein thesubstantially entangled plurality of fibers comprise Needle tackedfibers.
 5. The thermal insulator of claim 1, wherein the oxidizedpolyacrylonitrile fibers have a median fiber diameter of from 1micrometers to 100 micrometers.
 6. The thermal insulator of claim 5,wherein the oxidized polyacrylonitrile fibers have a median fiberdiameter of from 5 micrometers to 20 micrometers and a median fiberlength of from 25 millimeters to 75 millimeters.
 7. The thermalinsulator of claim 1, wherein the non-woven fibrous web recovers to atleast 70% of its original thickness 5 minutes after being compressed to37% of its original thickness at ambient conditions.
 8. A thermallyinsulated assembly comprising: a heat source; and a thermal insulator ofclaim 1 at least partially surrounding the heat source.
 9. A method ofmaking a thermal insulator comprising: mixing oxidized polyacrylonitrilefibers having crimped configurations with reinforcing fibers havingouter surfaces comprised of a polymer with a melting temperature between100° C. and 300° C.; heating the fiber mixture to a temperaturesufficient to melt the outer surfaces of the reinforcing fibers toprovide a non-woven fibrous web; and entangling the oxidizedpolyacrylonitrile fibers and reinforcing fibers with each other along adirection perpendicular to the non-woven fibrous web to provide anaverage bulk density of from 10 kg/m³ to 35 kg/m³ in the non-wovenfibrous web.
 10. A method of making a thermal insulator comprising:mixing oxidized polyacrylonitrile fibers with reinforcing fibers havingouter surfaces comprised of a polymer with a melting temperature between100° C. and 300° C. to obtain a non-woven fibrous web, wherein theoxidized polyacrylonitrile fibers represent over 85% by volume of fiberspresent that are not reinforcing fibers; heating the fiber mixture to atemperature sufficient to melt the outer surfaces of the reinforcingfibers to provide a non-woven fibrous web; and entangling the oxidizedpolyacrylonitrile fibers and reinforcing fibers with each other along adirection perpendicular to the non-woven fibrous web to provide anaverage bulk density of from 10 kg/m³ to 50 kg/m³ in the non-wovenfibrous web.
 11. The method of claim 9, further comprising smoothing amajor surface of the non-woven fibrous web by calendaring the non-wovenfibrous web, heating the non-woven fibrous web, and/or applying tensionto the non-woven fibrous web.
 12. The method of claim 11, wherein thenon-woven fibrous web further comprises a density gradient at thesmoothed surface.
 13. The method of claim 9, further comprising coatingthe non-woven fibrous web with a coating fluid selected from the groupconsisting of silicones, acrylates, and fluoropolymers whereby thenon-woven fibrous web has an emissivity of less than 0.5.
 14. A thermalinsulator made by the method of claim
 9. 15. A method of insulating anelectric vehicle battery comprising: providing an enclosure adjacent tothe electric vehicle battery; placing the thermal insulator of claim 1in compression within the enclosure; and allowing the thermal insulatorto expand and substantially fill the enclosure.